Electric motor control apparatus



Nov. 16, 1948. s. G. ISSERSTEDT ELECTRIC MOTOR CONTROL APPARATUS 3 Sheets-Sheet 1 Filed March 26, 1943 3 n vc n tor swam/0 6. 15.90% T0T Nov. 16, 1948. s. G. ISSERSTEQDT 2,453,917

ELECTRIC MOTOR CONTROL APPARATUS NOV. 16, 1948. 5, 5, [SSERSTEDT 2,453,917

ELECTRIC MOTOR CONTROL APPARATUS Filed March 26, 1943 3 Sheets-Sheet 3 CUNT/WLLE Y 3nventor imam/0 615551957207 Gttorneg' Patented Nov. 16, 1948 ELECTRIC MOTOR CONTROL APPARATUS Siegfried G. Isserstedt, Toronto, Ontario, Canada, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application March 26, 1943, Serial No. 480,672

16 Claims. 1

The present invention relates to control apparatus, and particularly to a controlling, indicating, or recording system wherein a reversible motor is controlled so as to position a load device in accordance with the changes of a'variable condition.

In such systems, it is frequently necessary to control a motor by means of a rather delicate and low-powered condition responsive device, as for example, a galvanometer or a compass needle. A common expedient in such systems is to periodically clamp or otherwise fix the sensitive condition responsive element and to provide mechanism which periodically performs a control function in accordance with the clamped position of the sensitive element. In such an arrangement, the sensitive element is not responsive to its controllin condition during the time'when it is clamped, and the control function is not performed in accordance with the position of the condition responsive element during the time when the element is free to move. The sensitivity of the system is therefore adversely affected by the periodical nature of the control effect produced.

It is therefore an object of the present invention to provide a control system operated by a sensitive condition responsive element in which means are provided for improving the sensitivity of the control system.

Another object of the present invention-is to provide an improved control system of the type wherein a sensitive condition responsive element is periodically clamped and the position of the clamped element is utilized to produce a control effect, wherein means is provided for prolonging the control effect beyond the duration of. the time during which the sensitive element is clamped, so as to increase the sensitivity of the system.

A further object of the present invention is to provide an improved system of the type wherein a pair of control contacts are intermittently moved into engagement to produce a control effect, wherein the control eflect produced by engagement of the contacts is substantially continuous regardless of the intermittent nature of the contact engagement.

A further object of the present invention is to provide improved means for intermittently stopping the motion of a sensitive control element.

Another object of the present invention is to provide, in a condition control system including a load device driven by a reversible motor, improved means for stopping motion of the load device instantaneously when the controller calls for a stop.

regardless of any tendency of the motor to overrun.

Other objects and advantages of the present invention will become apparent from a consideration of the appended specification, claims, and drawings, in which Figure 1 is a cross-sectional view .of a control instrument operated by a compass and including preferred features of my invention, V

Figure 2 is a cross-sectional view of a modified form of control device embodying my invention.

Figures 3, 4, and 5 illustrate, somewhat diagrammatically, three different forms of control systems which may be used with either of the control devices shown in Figures 1 and 2, and

Figure 6 shows a modified form of control system employing a somewhat different type of control device.

FIGURE 1 Referring now to Figure 1, there is shown a control instrument 28 including a casing I0 enclosing a compass needle II, which is provided with damping vanes l2 of conventional form. The compass needle I l is carried by a shaft l3 mounted in upper and. lower bearings i4 and i5, respectively. I

The upper bearing I4 is formed as part of a plug which is threaded through a hole in the center of an insulating plate l6 which covers the upper side of the casing iii. The bearing i5 is formed in a similar plug which threadedly engages the sides of a hole in the bottom of casing i0.

Shaft i3 is provided near its upper end with a flange i! which carries a collar it of magnetic material. The collar l8 may be keyed or otherwise fixed to the shaft i3.

The collar l8 supports, in any suitable manner, a flexible finger IS. The finger l9 carries at one end a flexible contact member 20 which is shaped like a broad U, having the bottom of the U attached to the finger Hi. There is also mounted on the finger l9, between the upwardly extending arms of the U-shaped contact 20, an armature 2 I, of magnetic material.

Imbedded in the lower base of the insulating cover plate l6 are a plurality of concentric contact segments 22, 23, and'jl. The segment 23 is in the form of a circle about the shaft i3. (See Fig. 3.) The segments 22 and 24 are arcuate,

and are concentric with the segment 23, but

spaced radially therefrom. An electromagnet 25, comprising a coil 26, surrounded on three sides by a channel shaped yoke 21, is also imbedded in the lower surface of the insulating 3 cover plate I6. The electromagnet 25 is also circular in form and is concentric with the contact segments 22, 23, and 24, about the shaft E3. The electromagnet 25 is spaced between the circular contact segment 23 and the outer contact segments 22 and 24, the arrangement being such that the electromagnet 25 is aligned with the armature 28 at all positions of pointer iii, while the contact segment 23 is aligned with the inner arm of the flexible contact 25 and either segment 22 or 24 may be aligned with other arm of contact 20, depending upon the angular position of pointer W. The segments 22, 23, and

24 are adapted for connection to electrical coni trol circuits by suitable conductors (not shown in Figure 1).. It will be readily understood that upon energization of electromagnet 25, armature 2| is attracted into engagement therewith, which engagement is permitted by the flexibility of the finger I9. As armature 2| moves into engagement' with electromagnet 25, the arms of the flexible contact 2|] are moved into engagement with the stationary contacts 22 and 23.

The housing i is provided with a circumferential gear 3|, cooperating with a gear 32 which may be driven by any suitable motor (not shown). pivotal support (not shown), so that upon rotation of gears 32 and 3|, the housing ii] is rotated.

It should be noted that the shaft i3 is elongated in order that the compass needle ii at its lower end may be separated substantially from the electromagnet 25 at its upper end to prevent undue disturbance of the compass needle by the field of the electromagnet 25. Also, a magnetic shield 35 is placed across the housing l0 Just under the finger H9. The purpose of this shield is to prevent any stray magnetic flux from the electromagnet 25 from reaching the compass needle Ii.

While I have indicated, for purposes of example' and description, that finger i9 is rotated by a compass, it should be readily apparent that a similar structure could be made responsive to any desired controlling condition, such as temperature, pressure, gravity, the position of a movable member, etc.

FIGURE 2 In Figure 2 is shown a compass operated controller mounted in a housing consisting of a lower cover portion 36, a base 37, and an upper cover portion 38. The lower cover portion 36 is threadedly attached to the base 31, and is provided with laterally extending cars 39 for mounting on any suitable support.

A compass needle 40 is carried by a shaft 4| which is supported on a thrust bearing 42 and extends upwardly through guide bearings 43 and 44, which are supported in spaced relation by the base 31.

The base 31 is provided with an upwardly extending central cylindrical portion 45. Supported on the upper surface of the cylindrical portion 45 is an electromagnet 45 of generally circular form, comprising a coil 41 in a channel shaped yoke 48.

The shaft 4| carries, above the upper surface of the cylindrical portion '45-, a finger 50. The finger carries an armature 5| aligned with the electromagnet 48. d

A collar 52, of insulating material, surrounds the cylindrical portion 45 and carries on its upper surface a plurality of contact segments 53 The housing i0 may be mounted on a 4 which correspond generally to the segments 22 and 24 of Figure i. For the sake of simplicity, only-a single segment 53 is shown in the drawing, although it should be readily understood that any desired number of segments might be used. The finger 55 is sufllciently long that its extremity overlies the contact segments 53. The construction is such that when electromagnet 45 is energized, the armature 5| is drawn down into engagement with it, the flexibility of finger 50 permitting such engagement. At the same time the extremity of finger an is drawn into contact with one of the segments 53. The lateral surface of the collar 52 carries a plurality of slip rings 54, each'of which is connected, by means not shown, to one 'of the segments 53. The surface of the collar 52 is also provided with a laterally projecting worm wheel 55, cooperating with a worm gear 56 which may be driven by a motor of any suitable construction (not shown).

A bracket 80 is mounted on the base 31 and supports an insulating block 6| which carries a plurality of brushes 52, each of which cooperates with one of the slip rings 54. Each brush 62 is connected by a conductor 63 to a terminal post 64 in a terminal panel 65 which is formed as an insert in the cover 38. Electrical conductors 56 are provided to connect the coil 47 of the electromagnet 46 to other terminals Bl on the terminal panel 55. Since the finger 50 is electrically connected to ground through the shaft 4| and the casing 35, it should be readily understood that upon engagement of finger 50 with any of the contact segments 53, an electrical circuit is completed between one of the terminals 64 and a conductor 53, brus'h 62, a slip ring 54, a contact segment 53, finger 50, and ground. Examples of suitable circuits which may be so controlled will be described in more detail hereinafter.

Fromm 3 Referring now to Figure3, there is shown an electrical control system in which a reversible motor I0 drives a suitable recording, indicating, or controlling mechanism H in response to a control instrument. similar to that shown in Figure'l.

In addition to the semi-circular contact segments 22 and 24 which appear in Figure 1, there is shown in Figure 3 an additional contact segment 29, which is intermediate the ends of segments 22 and 24.

The condition responsive instrument 28 electrically controls the energization of three relays 12, 13, and 14. The relay 12 comprises a winding 15, which is adapted to actuate a switch arm 16 cooperating with an in contact 11, a switch arm 18 cooperating with an outcontact i9, and a switch arm cooperating with an in contact 8|.

The relay 13 comprises an electrical windin 85, which controls the movements of a Switch arm 86 cooperating with an out contact 81. The relay 14 comprises a winding 88, which controls the movement of a switch arm 89, cooperating with an out contact 90, a switch arm 9|, cooperating with an in contact 92, and a switch arm 93 cooperating with an in contact 94.

The relays 12, 13, and 14 control the energization of motor 70. which comprises an armature 96 and a pair 01' field windings 91 and 98, which. when selectively energized control the rotation of motor Hi in opposite directions. The armature 98 is connected through an electrically operated clutch 99 and a gear train indicated schematically at I to mechanism 1| and gear 32, which engages gear 3! for bodily rotating the control instrument 28.

An interrupter |0|, comprising a coil I02, which controls the movements 01 a switch arm I03, cooperating with an out contact I04, is provided to control the energization of electromagnet 20.

Operation of Figure 3 Power for the control system shown in Figure 3 is obtained from suitable supply lines 0 and III. Although a legend has beenv applied to the drawing, indicating that line 0 is positive and that line I is negative, this is merely for convenience. It will be readily understood by persons skilled in the art that either an alternatin or a direct current supply could be used.

Coil of electromagnet 25 is periodically energized through a circuit which may be traced from positive supply line I I0 through a conductor H2, winding 28, the conductor II3, winding I02 of interrupter IOI, switch arm I03, contact I04, and a conductor II4 to negative supply line III. When this circuit is completed by engagement of switch arm I03 with contact I04, coil 26 is energized, thereby attracting the armature 2| and causing flexible contact member 20 to bridge the gap between circular contact segments 23 and one of the outer row of contact segments 22, 24, or 29. At the same time, winding I02 is energized to attract switch arm I03 and move it out of engagement with contact I04. When contact I03 is moved away from contact I04, the energizing circuit for electromagnet winding 28 is broken, thereby releasing armature 2| and causing flexible switch contact 20 to separate from the contact segments, thereby leaving finger i9 and shaft I3 free to rotate in accordance with the direction of the magnetic field or other variable condition to which they are responsive. It will be readily understood that the characteristics of interrupter I0| may be varied by means well known in the art so that the spacing of the intermittent energizations of coil 26, and the duration of such energizations, may be predetermined as desired.

When the finger I9 is in the position shown in I the drawing, and the electromagnet 25 is energized to cause engagement of contact member 20 with segments 23 and 29, an energizing circuit is completed for winding 85 of relay 13. This circuit may be traced from positive supply line ||0 through conductor I I5, contact segment 23, contact member 20, contact segment 29, relay winding 85, and a conductor I|8 to negative supply line III. Energization of winding 85 causes switch arm 88 to move out of engagement with contact 81. When the parts are in the positions shown in the drawing, no further control effect is produced. Under certain other conditions to be described, however, the separation of switch arm 86 from contact 81 is utilized to open holding circuits for the windings 15 and 88 of relays 12 and 14.

When the finger I9 is in the position shown in the drawing, the condition to which the finger I9 responds has the value which the system is to maintain. It is for this reason that no control effect is produced on the motor 10 when the finger I9 is in this position.

Let it now be assumed that the controlling condition changes so that the shaft I3 is rotated in a clockwise direction as viewed in Figure 3, and that this change continues until the contact member 20 moves above the contact segment 22. Then when the armature 2| is next attracted by the energization of the electromagnet 20, contact member 20 bridges the gap between segments 23 and 22, completing a circuit for the energizatlon of winding 15 of relay 12. This circuit may be traced from positive supply line 0 through conductor I I8, contact segment 23, contact member 20, contact segment 22, a conductor II1, winding 15, and conductor 8 to negative supply line III. This circuit is completed onl for a time corresponding to the time of energization of electromagnet 25. However, the energization of winding 15 causes switch arm 16 to move into engagement with contact 11, thereby completing a holding circuit for winding 15. This holding circuit may be traced from positive supply line |I0 through a conductor I I8, contact 81, switch arm 86, conductors I I3 and I20, contact 90, switch arm 89, conductor |2I-, switch arm 18, contact 11, a conductor I22, winding 15, and conductor 8 to negative supply line II I. This energization of winding 15 through the holdin circuit is maintained until either switch arm "moves out of engagement with contact 81, upon energization of winding 85 of relay 13, as previously described, or until switch arm 88 moves out of engagement with contact 90 upon energization of winding 88 of relay 14.

Energization of winding 15 of relay 12 also causes switch arm 18 to move out of engagement with contact 19, thereby opening a holding circuit for winding 88 of relay 14, to be later described in detail.

Energizatlon of winding 15 of relay 12 also causes switch arm to move into engagement with contact 8|, thereby completing an energizing circuit for motor 10 which may be traced from positive supply line 0 through a conductor I23, contact 8|, switch arm 80, a conductor I24, field winding 98 and armature 98 of motor 10, a'conductor I25, electrically operated clutch 99, and a conductor I28 to negative supply line I I I. Clutch 99 is so constructed that when energized, it connects motor 10 with the gear train I00 and thereby with the gear 32 and the mechanism 1|. Since the clutch 99 and the motor armature 98 are connected in series, the clutch is always energized whenever the motor is energized. When the motor is deenergized, the clutch is immediately deenergized, disconnecting the motor from its load and preventing the natural tendency of the motor to overrun from causing a corresponding overrunning of the mechanism 1| or the gear-32.

Energization of field winding 98 and armature 96 causes rotation of motor 10 in a direction such as to drive the gear 32 counter-clockwise, thereby driving the gear 3| clockwise, and moving the control instrument 28 so as to carry the contact segment 22 out from under the contact member 20 and bring the segment 29-under the contact member 20 again. When the motion of gear 3| has continued sufficiently to bring the segment 29 under the contact member 20, then on the next energization of electromagnet 25, the relay winding will be energized as previously described, resulting in an interruption of the holding circuit through relay winding 15, and a consequent deenergization of motor I0 and clutch 99, thereby stopping motion of the gear 3|.

It will be readily understood by those skilled in the art, that in certain types of control systems, the follow-up gears 3| and 32 may be omitted, as the operation of the control device 1| will be effective to change the controlling condition so as to bring the pointer I9 back to the normal posiment could be used, for example, where a mag- ,netic compass is used to control the operation of the rudder in an aircraft so as to maintain the craft on a predetermined compass course. Then, in the event of a deviation of the craft from its course, the controller It would be operated to turn the rudder until the position of the finger I9 indicated that the craft had been restored to its predetermined course.

Let it now be assumed that the controlling condition changes so as to move the shaft I3 counterclockwise, thereby moving the finger I9 also counter-clockwise from the position shown in the drawing until the contact member 20 moves above the contact segment 24. Then upon the next energization of electromagnet 25, an energizing circuit is completed for a winding 90 of relay I4. This energizing circuit may be traced from positive supply line IIO through conductor II5, contact segment 23,; contact member 20,

contact segment 24, a conductor I2I, winding 88,

and conductor III; to negative supply line III.

Energization of winding 68 causes switch arm 89 to move out of engagement with contact 90, thereby opening the holding circuit for relay circuit I5, if it has not been previously opened by energization of winding 85 of relay 53. Energization of winding 88 of relay I4 also causes switch arm 9I to move into engagement with contact 92, thereby establishing a holding circuit for winding 88 which may be traced from positive supply line IIII through conductor H8, contact 81, switch arm 86, conductors H9 and I28, switch arm 18, contact 19, a conductor I29, contact 92, switch arm 9|, a conductor I30, winding 88, and conductor II6 to negative supply line III. This holding circuit remains energized until'opened by separation of switch arm I8 from contact I9 upon energization of winding ."I of relay I2, or upon separation of switch arm 86 from contact 81, upon encrgization of winding 85 of relay I3.

Energization of winding 88 of relay I4 also causes switch arm 93 to move into engagement with contact 94, thereby completing an energizing circuit for motor III, which may be traced from positive supply line IIO through conductor I23, 'contact 94, switch arm 93, a conductor I3I, winding 91, armature 96, conductor I25, clutch 99, and conductor I26 to negativesupply line III. Energization of field winding 9'! and armature 96 of motor I0 causes rotation of motor I0 in a d rection so as'to drive the gear 32 in a clockwise direction, thereby moving gear 3| counter-clockwise and causing the control instrument 28 to follow the motion of the finger I9.

energized through the circuit previously traced whereby moving switch arm 86 out ofengagement with contact 81 and opening the holding circuit for winding 68 of relay I4, previously traced. Relay I4 is then deenergized, and motor 'I0 is stopped.

Summarizing, it should now be apparent that whenthe position of finger I9 is such that contact member 20 engages either contact segment,

22 or 24, motor I0 is energized for rotation in one direction or the other, and the rotation of motor I0 is maintained, regardlessof the intermittent nature of the contact between segments 22 and 24 and contact member 20, until the contact member 20 again engages the neutral contact segment 29. If by chance it should happen that while the holding circuit of either relay I2 or I4 was energized, the contact member 20, carried by finger I9, should move clear across the neutral contact segment 29 during one of the periods between successive energizations of electromagnet 25, then the next engagement of contact member 20 with segment 22 or 24 would cause deenergization of the previously established holding circuit for the relay I2 or I4, and the establishment of a new holding circuit for the relay corresponding to the contact segment 22 or 24 which is at the moment engaged by the contact member 20.

FIGURE 4 There is shown in Figure 4 a modification of the control system of Figure 3. In the control system of Figure 4 the condition responsive instrument 28 and the motor I0 correspond to the same elements in Figure 3, and have been assigned the same reference numerals. The relay system controlled by the instrument 28 is somewhat difierentthan that of Figure 3. There are shown in Figure 4 three relays I40, I, and I42, associated with the contact segments 22, 29, and 24 respectively. The relay I40 comprises a winding I43 controlling a switch arm I44 which cooperates with an out contact I45 and a switch arm I46, which cooperates with an in contact I41. The rela I4I comprises a windirig I which controls the movements of a switch arm I5I relative to an in contact I52 and an out contact I53. The relay I42 comprises a winding I54 which controls the operation of a switch arm I55 cooperating with an out contact I56 and a switch arm I51 cooperating with an in contact I58.

The relays I40 and I42 are of the fast make, slow release type. That is to say, when energized, the relays rapidly move their associated switch arms to their energized position, but upon deenergization, the switch arms move back to their normal deenergized position slowly or with a time delay. This method of operation may be accomplished by any desired structure, several of which are well known in the art. For example, the relay may be provided with a one-way dashpot arrangement, which slows the movement of the armature towards its deenergized position, but is not effective to slow the movement 01. the armature of the relay in the direction of its energized position,

Operation of Figure 4 When the finger I9 is in the position shown in the drawing, the gap between segment 23 and segment 29 is bridged upon energization of electromagnet 25. When this occurs, an energizing circuit is completed for winding I50 of relay III. This circuit'may be traced from positive supply line IIII through conductor II5, contact segment 23, contact member 20, contact segment 29, winding I50, and a conductor I60 to negative supply line III. Energization of winding I50 causes switch arm I5I to move into engagement with contact I52, thereby completing a holding circuit for winding I50, which may be traced from positive supply line IIO through a conductor I6l,

a conductor I62, switch arm I5I, contact I52, a conductor I63, switch arm I55, contact I56, conductor I64, switch arm I44, contact I45, 9. conductor I65, winding I50, and the conductor I60 29, until the holding circuit is broken by move-,

ment of switch arm I44 out oi engagement with contact I45, or by movement 'of switch arm I55 out of engagement with contact I50 as the resuit 01 energization of either relay winding I43 or I54, respectively.

When relay winding I50 is deenergized, the switch arm I5I moves into engagement with out contact I53, thereby completing an energizing circuit for clutch 99 between motor and its load. This'energizing circuit for clutch 99 may be traced from positive supply line IIII through I conductor I81 to negative suppl line III.

When the finger I9 is in a position such that energization of electromagnet 25 causes the contact member 20 to bridge the gap between segments 23 and 22, the bridging of that gap completes an energizing circuit for winding I43 of relay I40. This circuit'may be traced from positive supply line IIll through conductor II5, segment 23, contact member 20, contact segment 22, winding I43, and conductor I00 to negative supplyline III.

Energization of winding I43 causes switch arm I44 to move out of engagement with contact I45, thereby breaking the holding circuit for winding I50 of relay I4I, previousl traced. Energization of relay winding' I43 also causes switch arm I48 to move into engagement with contact I41, thereby completing an energizing circuit for motor 10. This energizing circuit may be traced from positive supply line IIIl through conductor IBI, contact I41, switch arm I45, a conductor I68, winding 88, armature 90, and conductor I61 to negative supply line I I I. Energization of motor field winding 98 causes rotation of motor 10 in a direction to drive gear 32 in a counter-clockwise direction, thereby driving gear iii in .a' clockwise direction and moving contact segment 29 to follow the movement of finger I9. Since winding I50 of relay MI is at this time deenergized, switch arm I5I engages contact I53, thereby completing the energizing circuit for clutch 99. Energiza tion of clutch 99.completes the mechanical connection between the motor 10 and the gear 32.

Although the energization of relay I40 by engagemcnt of contact member 20 with contact segment 22 is intermittent, the energization of motor 10 is prolonged beyond the period of engagement of contact member 20 and contact segment 22 because of the fast make, slow release charactcristic of relay I40. Furthermore, since the clutch 99 remains energized continuously until the contact member 20 again engages contact 29, the natural overrun of the motor after its deenergization is utilized to drive the gears 32 and 3| further in the proper direction to follow the motion of finger I9. By proper design of relays I40 and I42, and coordination of their characteristics with those of interrupter IIlI, the driving of gear 32 and mechanism H by the moto may be made substantially continuous whenever the contact member 20 is maintained above either segment 22 or 24.

When finger I9 is in such a position that contact member 20 engages contact segment 24 i'pon energization of electromagnet 25, an energizing circuit is completed for winding I54 of relay I42. This circuit may be traced from positive supply line IIO through conductor III, contact segment 23, contact member 20, contact segment 24, winding I54, and conductor I80 to negative supply line III. Energization of winding I54 causes switch arm I55 to move out of engagement with contact I55, thereby opening the holding circuit for winding I50 of relay I. previously traced.

Energization of winding I54 also causes switch arm I51 to move into engagement with contact I58,,thereby completing an energizing circuit for motor 10, which may be traced from positive supply line IIO through conductor IGI, contact I58, switch arm I51, a conductor I09, field winding 91 and armature 96 or motor 10, and conductor I61 to negative supply line I I I.

Deenergization of winding l50 of relay I4I allows switch arm I5I to engage contact I53, thereby energizing the clutch 99 through the circuit previously traced and connecting motor 10 with mechanism II and gear I2. Energization of field winding 91 and armature 86 causes motor 10 to drive gear 32 in a clockwise direction, rotating gear 3| counter-clockwise and causing contact segment to follow the motion of finger I9.

From the foregoing, it should be apparent that in the system of Figure 4, the overrun of the motor is advantageously utilized to drive the followup mechanism as lon as the controlling condition is diflerent from its desired value, but as soon as the controlling condition reaches its desired value, the motor is declutched from its load so thatthe overrun of the motor will not cause the follow-up systemto overshoot.

Freon:

In Figure 5 is shown another modification of the control system oi Figure 3. In Figure 5, the follow-up tionnection between the motor 10 and the condition responsive control instrument is omitted. Also, the clutch between the motor 10 "and the mechanism H, which it drives, is omitted. All parts which are equivalent to the corresponding parts in Figure 3 have been given the same reference numerals in both Figures 3 and 5.

The sensitive control instrument I14 of Figure 5 differs from the instrument 29 of Figure 3 in that two intermediate contact segments I15 and I18 are spaced between the ends of segments 22. and 24, the latter pair of segments being shortened to accommodate the two segments which replace the single segment 29 of Figure 3.

'The condition responsive instrument I14 controis the motor 10 through four relays, I11, I18, I19, and I80, which are associated with contact segments 22, I15, I16, and 24 respectively. The relay I11 comprises a winding I8I which controls the movement of a switch arm I82 relative to a cooperating in contact I83, and the movements of a switch arm I84 relative to a cooperating in contact I85 and a cooperating out contact I85. The relay I18 comprises a winding I81 which controls the movements of a switch arm I88 rela- 1i Operation of Figure 5 When the finger I9 is in the position shown in the drawing, the contact member 20 1s not engaging any of the segments 22, 24, I15, or I19,

nor does it engage any of those segments when ber 20 bridges the gap between segments 23 and I15, thereby completing an energizing circuit for winding I81 of relay I10. This circuit may be traced from positive supply line i it) through conductor II5, segment-23, contact member 20, segment I15, winding I81, and a conductor 205 to the negative supply line iii. Energization of winding I81 of relay I18 causes movement of switch arm I08 into engagement with contact I89, thereby completing an energizing circuit for winding 98 of motor 10. This energizing circuit may be traced from positive supply line H0 through a conductor 209, switch arm i88, contact I89, a conductor 201, field winding 98, armature 96, and a conductor 208 to negative supply line III. armature 96 of motor 10 causes the motor to run in the direction indicated by the sense in which the controlling condition varies from its predetermined value. It should be noted that there is no holding circuit associated with relay I18, so that as long as contact member 20 engages contact segment i intermittently, the motor 19 is energized through thewinding 99 intermittently.

Let it now be assumed that the controlling con.. dition continues to vary in the same sense, thereby causing further clockwise movement of finger I9 so that the contact member 20 is gradually moved to a point where it engages contact seg-. ment 22 when the armature 26 is attracted upon energizationof electromagnet 25. As soon as contact member 20 engages contact segment 22, an energizing circuit is completed for winding Hill of relay i11. This energizing circuit may be traced from pr 3itive supply line i [l9 through conductor II5, segment 23, contact member 20, contact segment 22, winding tilt, and conductor 205 to negative supply line Mi. 1

Energization of winding i8i causes switch arm 998 to move into engagement with contact I83, thereby completing an energizing circuit for winding 98 and armature 96 of motor 18. This circuit may be traced from the positive supply line iI0 through conductor 206, switch arm Hi2, contact I83, conductor 201, field winding 98, armature 96 and conductor 208 to negative supply line III.

Energization of winding I8I of relay l1! also causes movement of switch arm I84 into engagement with contact I85. This completes a holding circuit for winding I8I which may be traced from positive supply line' IIO through conductor 206, switch arm I88, contact I90, a conductor 209, switch arm I94, contact i95, a conductor 2 I0, con tact 20I, switch arm I99, a conductor 2i I, switch arm I84, contact I95, a conductor '2I2, winding I8I, and conductor 205 to negative supply line III. Winding I8I therefore remains energized until its holding circuit is broken either at contact I90, I95, or 20I, which might occur upon energization of relays I18, I19, or I80, respectively, Therefore when the contact member 20 engages contact segment 22, the motor is con- Energlzation of field winding 98 and tinuously energized regardless of the intermittent nature of the contact between contact member 20 andcontact segment 22.

Let it now be assumed that the controlling condition changes in such a sense that finger I9 moves in a counterclockwise direction so that upon energization of electromagnet 25, contact member 20 movesinto engagement with contact segment I16. This completes an energizing circuit for Winding I9I of relay I19. This energizing circuit can be traced from positive supply line IIO through conductor II 5, contact segment 23, contact member 20, contact segment I16, winding I9I and conductor 205 to negative supply line III.

Energization of winding I9I of relay I19 causes the switch arm I 92 to move into engagement with contact I93, thereby. completing an energizing circuit for field winding 91 and armature 90 of motor 10. This motor energizing circuit may be traced from the positive supply line II 0 through conductor 206, switch arm I92, contact l93, a conductor 2I3, field winding 91, armature 99, and conductor 208 to negative supply line III.

relay I19, motor 10 is intermittently energized as long as the finger I9 remains in a position where contact member 20 is aligned with contact I56, this intermittent energization being produced by the action of electromagnet 25.

Now consider that the controlling condition causes finger I9 to move further in a counterclockwise direction untilthe contact member 20 reaches a position aligned with the contact segment 24. Then upon the next energization of electromagnet 25, contact member 20'bridges the gap between contact segments 23 and 24, thereby completing an energizing circuit for winding I96 of relay I80. This energizing circuit can be traced from the positive supply line I I0 through conductor II5, contact segment 23, contact member 20, contact segment 24, winding I96, and conductor 205 to negative supply line I I I.

Energization of winding I96 of relay I80 causes switch arm I91 to move into engagement with contact i98, thereby completing an energizing circuit for field winding 91 and armature 96 of motor 10, This circuit may be traced from the 'positive supply line IIO through conductor 2,06,

switch arm I91, contact I98, conductor 2I3, field winding 91, motor armature 96, and conductor 209 to negative supply line I I I.

Energization of winding I96 of relay I80 also causes switch arm I99 to move into engagement with contact, 200, thereby establishing a holding circuit for windin I96. This holding circuit may be traced from positive supply line IIO, through conductor 206, contact arm I88, contact I90, con-' ductor 209, switch arm I94, contact I95, conductor 2I0, contact I86, switch arm I84, conductor 2| I, switch arm I99, contact 200, a conductor 2", winding I96, and conductor 205 to negative supply line III. This holding circuit remains energized, keeping the motor 10 continuously energized until the holding circuit is broken at either contact I86, contact I90, or contact I95, which breaking of the holding circuit occurs upon energization of any of relays I11, I18, or I19, respectively.

From the foregoing, it should be apparent that in the system of Figure 5, the motor 10 is intermittently energized when the controlling condition departs a small amount from the predetermined value which the system is to maintain,

Since there is no holding circuit associated with the desired value.

From: 6

The control system shown in Figure 6 illustrates the application ofsome oi the principles of my invention to a system of a type somewhat different than that previously described. In Figure 6, a sensitive condition responsive elementinot shown) moves a contact finger 225 about a pivot 226. -The extremity of the finger 225 overlies and is normally spaced from a resistance element 221. The finger 225 carries, at an intermediate point, an armature 228, which is aligned with an electromagnet 229, of generally arcuate form. The arrangement may correspond generallyto the condition responsive switching arrangement shown in Figure 1, except that the contact segments 22 and 24 have been replaced by} the resistance element 221, The finger 225 corresponds generally to finger l9 and the electromagnet 229 corresponds to the electromagnet 25 of Figure 1.

The finger 225 and the resistance 221 form a control potentiometer 23] which is a part of a normally balanced electrical control network generally indicated 236. The network 230 also includes a rebalancing potentiometer 232-, which comprises a resistance element 233 and a slider contact 234, which moves along the resistance element 233 upon rotation of the shaft 235 on which the slider 234 is mounted.

The network 230 is supplied with electrical energy from any suitable source which is shown as a battery 236 having one of its terminals connected to the finger 225 by a conductor 231, and its other terminal connected to the slider 234 by a conductor 238.

The network 238 includes a pair of output terminals 246 and 2, which are at the same potential when the network is balanced. The network is balanced whenever the finger 225 andv the slider 224 are at corresponding positions along their respective resistances 221 and 233. Protective resistances 242 are provided in each of the branches of the network in order to prevent connected to output terminal 240 of network 230 by a conductor 25!. The control electrode 249 ofdischarge device 244 is connected through output terminal 24l of network 230 by a conductor 252.

The discharge devices 243 and 244 control the energization of a motor indicated generally as 255, and including an armature 256 and a pair of field windings 251 and 258 which control the energization of the motor in opposite directions. The motor 255 is connected through an electrically operated clutch 259 to the shaft 235 which operates slider 234 of the rebalancing potentiometer 232 and a recording, indicating, or controlling mechanism schematically indicated at 260.

The cathodes 241 and 258 may be heated by any suitable source of electrical energy, as for example, the batteries 26! and 262 shown on the drawing. Cathodes 241 and 250 are connected through a conduct or 253 to the negative supply line 264 which is grounded at 265. The control electrodes 246 and 248 are supplied with a biasing potential by means 'of a battery 266, which is connected between conductor 263 and the output terminals 246 and 2" of network 238. A pair of resistances 261 and 268 are connected between the negative 'terminal of battery 266 and each of the terminals 246 and 241.

Power is supplied to the electromagnet 228 and to the motor 255 from a pair of direct current supply lines 218 and 264. The supply of energy to these devices is interrupted at suitable'intervals, to be more completely described later, by means of a commutator device shown generally as 21!, which is continuously driven by a motor 212 having a field winding 213 and an armature 214 connected in series between the supply lines 210 and 264 by means of conductors 215 and 216. The commutator device 21! comprises an arm 215 rotating with a shaft 216 andcarrying a set of three brushes 211, 218, and 219. The brush 211 cooperates with a contact segment 280 concentric with the shaft 216. The brush 218 cooperates with a pair of short arcuate contact segments 28! and 282, which are also concentric with the shaft 216. The brush 219 cooperates with a pair of long arcuate segments 283 and 284, which are also concentric with the shaft 216 and which have gaps between their ends substantially aligned with the short arcuate segments 28! and 282.

Operation of Figure 6 supply line 210 through a conductor 290, contact segment 280, brush 211, commutator arm 215,

brush 219, segment 283 ,or 284, a conductor 29!, clutch 259, aconductor 292, armature 258 of motor 255, and either field winding 251 or 258 to anode 2545 or 248. 244 remain nonconducting at this time, no current flows through the connection just traced and the motor remains stationary.

When the network 230 is balanced, the output terminals 240 and 24! are at the same potential, so that no current flows through the connection including the resistances 261 and 268. At that time the only potential supplied to the control electrodes 246 and 249, is that supplied by the biasing battery 266, which is of a polarity and magnitude such as to prevent the initiation of a discharge through the devices 243 or 244.

- Since the finger 225 isnormally spaced from the resistance 221. there is normally no current flowing through the network 236, and hence, no unbalance potential at the output terminals 249 and 2. The electromagnet 229 is periodically energized, however, and upon such periodical energization, the tip of finger 225 is moved into engagement with resistance 221, so that electrical energy is supplied to the network 230 from the battery 236. The energizing circuit for electromagnet 229 may be traced from positive supply line 218 through conductor 290, contact segment 280, brush 211, commutator arm 215, brush 218, either contact segment 28! or 282, a conductor 293, electromagnet 229, and a conductor 294 to ground at 295. Since the supply line 264 is grounded at 265, when this circuit is completed If the discharge devices 243 and' 15 or 282, the electromagnet 228 is connected across the supply lines. The commutator arm 215 ro tates in a clockwise direction, as indicated by the legend in the drawing.

It should be noted that the relative position of the contact segments 28l and 282 with respect to the positions of the segments 283 and 284 are such that the electromagnet 229 is energized Justbefore the positive voltage is applied to the anode 245 and 248 of the discharge devices 243 and 244. This relative position is chosen so that the inherent lag of the electromagnet 229 insures that the tip of finger 225 engages the resistance 221 at the moment when the'positive potential is first applied to the anodes 245 and 248. If desired, the segments 2M and 282 may be adjustably mounted so that they may be moved to their optimum position with respect to segments 283 and 284.

If the bridge circuit 238 is unbalanced, due to a change in the controlling conditions, at the time when finger 225 engages resistance 22'l, a potential difference is set up between the output terminals 240 and 24!. For example, if the finger 225 is moved to the left from the position shown more negative than terminal 24i| since there is less resistance between it and the negative terminal of the battery 238. Thereforea voltage drop exists across boththe resisters 251 and 288 in such a sense that their right hand terminals are positive with respect to their left hand terminals. The potential drop across resistance 281 is then in the same sense as that of the battery 256 as far as the connection between the cathode 241 and the control electrode 248 of the discharge device 243 is concerned. Therefore the control electrode 246 is made more negative than before and the discharge device 243 is prevented from becoming conductive. In the connection between cathode 258 and grid 249, however, the potential drop across resistance 258 is in a, sense opposite to that of the drop across biasing battery 266. The potential of control electrode 249 is thereby made more positive. If the battery 256 has been so chosen as to just maintain the devices .243 and 244 cut oil, the addition of thispositive potential devices 243 and 244 are of the gaseous type wherein when a discharge has been initiated, it is maintained until the anode-cathode circuit is opened, regardless of the potential applied to the control electrode. Therefore, if a discharge is initiated in the device 244 at the same time that a positive potential is applied to the anode 248, the device 244 is rendered conductive and remains conductive until the anode-cathode circuit is opened by the movement of brush 219 past th end of the contact segment 283 or 284.

It will be readily understood that if the network 230 is unbalanced in the opposite sense, i. e., so that outputv terminal 24! is negative with respect to output terminal 240, then when the pointer 225 engages slider 221, the discharge device 243 becomes conductive, due to the positive potential applied to its control electrode 246.

When the discharge device 244 is conductive, the current flow through the armature 258 and field windings 258 of motor 255, and through the electrically operated clutch 259, causing the lat ter to connect the motor 255 to its load. Energizatlon of armature 256 and field winding 258 causes the motor 255 to drive the shaft 235 countar-clockwise, thereby moving slider 234 to the 225 does not correspond to that of slider 234 when th'e electromagnet 229 is energized, either'discharge device 243 or 244 breaks down, causing energization of motor 255 to drive the slider 234 in theproper direction to rebalance the network By intermittently energizing the network'238 in this way, I am able to use a much higher potential on the network 238 with no greater heating or resistance loss, than could be used if the "While I have shown and described certain pre- -ferred embodiments of my invention, other modiflcations thereof will readily occur to those skilled in the art, and I therefore wish my invention to be limited only by the appended claims.

I claim as my invention:

1. Electrical control apparatus, comprising in combination, relatively stationary and movable contact means, condition responsive means for movin said movable contact means through a path parallel to and spaced from said stationary contact means, time-controlled means for periodically causing engagement of said contact means, an electrical control device, means responsive to engagement of said contact means to initiate energization of said control device, and means effective to maintain energization of said control device after initiation thereof for a period longer than the time of engagement of said contacts While said condition responsive means is free to move said movable contact means.

2. Electrical control apparatus, comprising in combination, a movable contact, a plurality of contacts normally spaced from and stationary with respect to said movable contact, an electrical control device, means responsive to a condition indicative of the need for operation of said control device for moving said movable contact along a path parallel to and spaced from said stationary contact, time-controlled means for periodically causing engagement of said movable contact with said stationary contacts, means responsive to engagement of a first of said plurality of contacts by said movable contact to initiate energization of said control device for operation in a predetermined sense, means responsive to engagement of a second of said plurality of contacts by said'movable contact to initiate energization moving said movable contact means along a path parallel to and spaced from said stationary contact means, said movable contact means normally having a predetermined neutral position on said path, time-controlled means for periodically causing engagement of said movable contactmeans with said stationary contact means, means responsive to engagement of said movable contact means with said stationary contact means at a point displaced from said neutral position to initiate energization of said control device for op eration in a sense dependent upon the direction of such displacement, and means efiective to maintain energization of said control device after initiation thereof for a period longer than the time of engagement of said contacts while said condition responsive means is freeto move said movable contact means.

4. Electrical control apparatus, comprising in combination, a movable contact, a plurality of contacts normally spaced from and stationary with respect to said movable contact, an electrical control device, means responsive to a condition indicative of the need for operation of said control device for moving said movable contact along i 2,453,917 I s combination, a movable contact, a plurality of contacts normally spaced from and stationary with respect to said movable contact, an electrical control device, means responsive to a condition indicative of the need for operation of said control device for moving said movable contact along a path parallel to and spaced from said stationary contacts, time-controlled means a path parallel to and spaced from said stationary I contacts, time-controlled means for periodically causing engagement of said movable contact'with said stationary contacts, first relay means for controlling energization of said control device for operation in a predetermined sense, second relay means for controlling energization of said control device for operation in an opposite sense, means including a first electrical circuit completed upon engagement of said movable contact with a first of said plurality of contacts for energizing said first relay means, means including a second electrical circuit completed upon engagement of said movable contact with a second of said plurality of contacts for energizing said second relay means, and holding circuit means for each of said relay means effective to maintain the energization thereof for a period longer than the time of engagement of said contacts.

5. Electrical control apparatus, comprising in combination, a movable contact, a plurality of contacts normally spaced from and stationary with respect to said movable contact, an electrical control device, means responsive to a condition indicative of the need for operation of said control device for moving said movable contact along a path parallel to and spaced from said stationary contacts, time-controlled means for periodically causing engagement of said movable contact with said stationary contacts, first relay means for controlling energization-of said control device for operation in a predetermined sense, second relay means for controlling energization of said control device for operation in an opposite sense, means includin a first electrical circuit completed upon engagement of said movable contact with a first of said plurality of contacts for energizing said first relay means, means including a second elecfor periodically causing engagement of said movable contact with said stationary contacts, first relay means for controlling energization of said control device for operation in a, predetermined sense, second relay means for controlling energization of said control device for operation in an opposite sense, means including a first electrical circuit completed upon engagement of said movable contact with a first of said plurality of contactsfor energizing said first relay means, means including a-second electrical circuit completed upon engagement of said movable contact with a second of said plurality of contacts for energizing said second relay mean holding circuits for said first and second relay means, switch means operated upon energization .of

either of said relay means to interrupt the hold-' ing circuit of the other relay means, third relay means operative upon energization thereof to interrupt both said holding circuits, and means including a third electrical circuit completed upon engagement of saidmovable contact with a third of said plurality of contacts intermediate said first and second contacts for energizing said third relay means.

1 '7. Electrical control apparatus, comprising in combination, movable contact means, stationary contact means normally spaced from said movable contact means, an electrical control device, means responsiveto a condition indicative of the need for operation of said control device for moving said movable contact means along a path parallel to and spacedafrom said stationary contact means, said movable contact means normally having a predetermined neutral position on said path, time-controlled means for perioditrical circuit completed upon engagement of said movable contact with a second of said plurality of contacts for energizing said second relay means, holding circuits for said first and second relay means, third relay means operative upon energization thereof to interrupt both said holding circuits, and means including a third electrical circuit completed upon engagement of said movable contact with a third of said'plurality of contacts intermediate said first and second contacts iorenergizing said third relay means.

6. Electrical control apparatus, comprising in cally causing engagement of said movable contact means with said stationary contact means, a pair of electrical discharge devices, each including an input circuit and an output circuit, and having a. characteristic such that upon initiation of a discharge therethrough, the discharge is maintained until said output circuit is effectively deenergized, means responsive to engagement of said movable contact means with said stationary contact means at a point displaced from said neutral position for initiating a discharge in one of said discharge devices selectively in accordance with the direction of such displacement, means connected in said output circuits for causing operation of said control device in a sense dependent upon the relative conductivity or said discharge devices, and means for periodically effectively deenergizing said output circuits.

8. Electrical control apparatus, comprising in combination, movable contact means, stationary contact means normally spaced from said movable contact means, an electrical control device, means responsive to a condition indicative of the need for operation of said control device for moving said movable contact means along a path parallel to and spaced from said stationary contact means, said movable contact means normally having a predetermined neutral position on said path, time-controlled means for periodically '75 causing engagement of said movable contact input circuit and an output circuit, and having a characteristic such that upon initiation of a discharge therethrough, the discharge is maintained until said outputcircult is effectively de-'- energized, means responsive to engagement of laid movable contact means with said stationary contact means at a point displaced from said neutral position for initiating a discharge in one or said discharge devices selectively in accordance with the direction of such displacement, means connected in said output circuits for causing operation of said control device in a sense dependent upon the relative conductivity of said discharge devices, and means associated with said, time-controlled means for deenergizing and reenergizing said output circuits in timed relation with the periodical engagements of said contact means.

9. Electrical control apparatus, comprising in combination, a movable contact, a plurality of contacts normally spaced from and stationary with respect to said movablecontact, an electrical control device, means responsive to a condition' indicative of the need for operation of said control device for moving said movable contact along a path, parallel to and spaced from said stationary contacts, time-controlled means for periodically causing engagement of said movable contact with said stationary contacts, means responsive to engagement of a first of said plurality of cpntacts by said movable contact toinitiate energization of -said control device for operation in a predetermined sense, means responsive to engagement of a second of said plurality of contacts by said movable contact to initiate energization of said control device for operation in an opposite sense, and means effective to maint-ain energization of said control device after initiation thereof for a period longer than the time of engagement of said contacts, said last named means comprising slow-release relay means associated with each of said energization initiating means.

10. Electrical control apparatus, comprising in combination, a movable contact, a pair of contacts normally spaced from and stationary with respect to said movable contact, a reversible electrical motor, means responsive to a condition indicative of the need for operation of said motorfor moving said movable contact along a path parallel to and spaced from said stationary contacts, time controlled means for periodically causing engagement of said movable contact with said stationary contacts, a pair of relays for selectively controlling the operation of said motor in opposite directions, energizing circuits for each of said relays; each said circuit comprising said movable contact and one of said stationary contacts, holding circuits for each of said relays, and switch means operated upon energization of either relay to interrupt the holding circuit of the other relay.

11. Electrical control apparatus, comprising in combination, a movable contact, a row of at least three contacts normally spaced from and stationarywith respect to said movable contact, a reversible electrical motor, means responsive to a condition indicative of the need for operation of said motor for moving said movable contact along a path parallel to and spaced from said stationary contacts, time-controlled means for periodically causing engagement of said movable contact with said stationary contacts, a pair oi ing circuits i'or each of said relays, switch means operated upon energization of either relay to interrupt the holding circuit or the other relay, a third relay, an energizing circuit for said third relay comprising said movable contact and a contact substantially at the center of said row, and switch means operated upon energization of said third relay to interrupt both said holding circuits.

12, Electrical control apparatus, comprising in combination, a movable contact, a row of four contacts normally spaced from and stationary with respect to said movable contact, a reversible electrical motor, means responsiye to a condition indicative of the need for operation of said motor for moving said movable contact along a path parallel to and spaced from said stationary contacts, time-controlled means for periodically causing engagement of said movable contact with said stationary contacts, and means for selectively controlling the operation of said motor in opposite directions in accordance with the direction of displacement of said movable contact from the center of said row, said last-named means comprising means responsive to engageinent of said movable contact with either of the stationary contacts at the ends of said row for causing continuous operation of said motor, and means responsive to engagement of said movable contact with either of the stationary contracts adiacent the center of said row for causing intermittent operation of said motor only during said periods of engagement.

, 13. Electrical control apparatus, comprising in combination, a movable contact, a row of four contacts normally spaced from and stationary with respect to said movable contact, a reversible electrical motor, means responsive to 'a consaid four contacts, holding circuits for each of the relays associated with the stationary contacts at the ends of saidrow, switch means operable upon energization of another of said relays for interrupting said holding circuits, and means for selectively controlling the operation of said motor in opposite directions in accordance with the direction of displacement oi said movable contact from the center of said row.

14. Electrical control apparatus, comprising in combination, a stationary member, a member movable along a path substantially parallel to and spaced from said stationary member, condition responsive means for causing movement of said movable member, first contact means on said stationary member comprising a pair of parallel elongated contact arrangements laterally spaced and having their long dimension parallel to saidarrangements, elongated electromagnet means extending parallel to said pair of elongated contact arrangements, armature means carried by 21 said movable member in alignment with said electromagnet means, and means for periodically energizing said electromagnet means.

15. Electrical control apparatus, comprising in combination, an electrical motor, control means for said motor including a pair of contacts, time controlled means for periodically causing engagement of said contacts, further means for relatively positioning said contacts, and means effective to maintain the energization of said motor ior a period longer than the time of engagement of said contacts to enable said further means to position said contacts while said motor is still energized.

16. Electrical control apparatus, comprising in combination, an electrical motor, a load device to be driven by said motor, clutch means for connecting said motor and said load device, a movable contact, a plurality of contacts normally spaced from and stationary with respect to said movable contact, means responsive to a condition indicative of the need for operation of said control device for moving said movable contact along a path parallel to and spaced from said stationary contacts, time-controlled means for periodically causing engagement of said movable 20 Number contact with said stationary contacts, said movable contact normally having a neutral position on said path opposite one 01 said plurality of contacts, means responsive to engagement of said movable contact with said one contact to cause operation of said clutch means to disconnect said motor and said load device, and means responsive to engagement of said movable contact with another of said plurality of contacts to cause energization of said motor and operation or said clutch means to connect said motor and said.1oad device.

SIEGFRIED G. ISSERGTEDT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Sperry Oct. 8, 1929 Schleicher et a1. Sept. 20, 1930 1,730,951 1,774,673 1,939,775 1,997,412 Fischel Apr. 9, 1935 Newell June 29, 1937 Holmes Dec. 19, 1933 4 

